samedi 2 juin 2012

Enceladus Plume is a New Kind of Plasma Laboratory












NASA / ESA - Cassini Mission to Saturn patch.

June 2, 2012

Recent findings from NASA's Cassini mission reveal that Saturn's geyser moon Enceladus provides a special laboratory for watching unusual behavior of plasma, or hot ionized gas. In these recent findings, some Cassini scientists think they have observed "dusty plasma," a condition theorized but not previously observed on site, near Enceladus.

Data from Cassini's fields and particles instruments also show that the usual "heavy" and "light" species of charged particles in normal plasma are actually reversed near the plume spraying from the moon's south polar region. The findings are discussed in two recent papers in the Journal of Geophysical Research.

"These are truly exciting discoveries for plasma science," said Tamas Gombosi, Cassini fields and particles interdisciplinary scientist based at the University of Michigan, Ann Arbor. "Cassini is providing us with a new plasma physics laboratory."


Image above: Cassini imaging scientists used views like this one to help them identify the source locations for individual jets spurting ice particles, water vapor and trace organic compounds from the surface of Saturn's moon Enceladus. Image credit: NASA/JPL/Space Science Institute.

Ninety-nine percent of the matter in the universe is thought to be in the form of plasma, so scientists have been using Saturn as a site other than Earth to observe the behavior of this cloud of ions and electrons directly. Scientists want to study the way the sun sends energy into Saturn's plasma environment, since that jolt of energy drives processes such as weather and the behavior of magnetic field lines. They can use these data to understand how Saturn's plasma environment is similar to and different from that of Earth and other planets.

The small, icy moon Enceladus is a major source of ionized material filling the huge magnetic bubble around Saturn. About 200 pounds (about 100 kilograms) of water vapor per second – about as much as an active comet – spray out from long cracks in the south polar region known as "tiger stripes." The ejected matter forms the Enceladus plume – a complex structure of icy grains and neutral gas that is mainly water vapor. The plume gets converted into charged particles interacting with the plasma that fills Saturn's magnetosphere.

Dark Moon, Dramatic Plume

Image above: Below a darkened Enceladus, a plume of water ice is backlit in this view of one of Saturn's most dramatic moons.

The nature of this unique gas-dust-plasma mixture has been revealed over the course of the mission with data from multiple instruments, including the Cassini plasma spectrometer, magnetometer, magnetospheric imaging instrument, and the radio and plasma wave science instrument. What scientists found most interesting is that the grains range continuously in size from small water clusters (a few water molecules) to thousandths of an inch (100 micrometers). They also saw that a large fraction of these grains trap electrons on their surface. Up to 90 percent of the electrons from the plume appear to be stuck on large, heavy grains.

In this environment, Cassini has now seen positively charged ions become the small, "light" plasma species and the negatively charged grains become the "heavy" component. This is just the opposite of "normal" plasmas, where the negative electrons are thousands of times lighter than the positive ions.

In a paper published in the December issue of the journal, a team of Swedish and U.S. scientists on the Cassini mission examined radio and plasma wave science instrument observations from four flybys of Enceladus during 2008. They found a high plasma density (both ions and electrons) within the Enceladus plume region, although the electron densities are usually much lower than the ion densities in the plumes and in the E ring. The team concluded that dust particles a hundred millionth to a hundred thousandth of an inch (a nanometer to micrometer) in size are sweeping up the negatively charged electrons. The mass of the observed "nanograins" ranges from a few hundred to a few tens of thousands of atomic mass units (proton masses), and must therefore contain tens to thousands of water molecules bound together. At least half of the negatively charged electrons are attached to the dust, and their interaction with the positively charged particles causes the ions to be decelerated. Because the dust is charged and behaves as part of the plasma cloud, this paper distinguishes this state of matter from dust that just happens to be in plasma.

Rings and Enceladus

Image above: A crescent Enceladus appears with Saturn's rings in this Cassini spacecraft view of the moon.

"Such strong coupling indicates the possible presence of so-called 'dusty plasma', rather than the 'dust in a plasma' conditions which are common in interplanetary space," said Michiko Morooka from the Swedish Institute of Space Physics, lead author of the paper and a Cassini radio and plasma wave science co-investigator. "Except for measurements in Earth's upper atmosphere, there have previously been no in-situ observations of dusty plasma in space."

In a dusty plasma, conditions are just right for the dust to also participate in the plasma's collective behavior. This increases the complexity of the plasma, changes its properties and produces totally new collective behavior. Dusty plasma are thought to exist in comet tails and dust rings around the sun, but scientists rarely have the opportunity to fly through the dusty plasma and directly measure its characteristics in place.

A separate analysis, based on data obtained by the Cassini plasma spectrometer, revealed the presence of nanograins having an electric charge corresponding to a single excess electron. "The Cassini plasma spectrometer has enabled us to discover and analyze new classes of charged particles that were wholly unanticipated when the instrument was designed and built in the 1980s and 90s," said Tom Hill, the study's lead author and a co-investigator based at Rice University in Houston.

Brilliant Enceladus

Image above: The Cassini spacecraft looks at a brightly illuminated Enceladus and examines the surface of the leading hemisphere of this Saturnian moon.

The nature of the Enceladus plume has been revealed over time due to the synergistic nature of the fields and particles instruments on Cassini, which has been in residence in Saturn's magnetosphere since 2004. Following the original detection of the plume based on magnetometer measurements, Sven Simon from the University of Cologne, Germany, and Hendrik Kriegel from the University of Braunschweig, Germany, found that the observed perturbation of Saturn's magnetic field required the presence of negatively charged dust grains in the plume. These findings were reported in the April and October 2011 issues of Journal of Geophysical Research Space Physics. Previous data obtained by the ion and neutral mass spectrometer revealed the complex composition of the plume gas, and the cosmic dust analyzer revealed that the plume grains were rich in sodium salts. Because this scenario can only arise if the plume originated from liquid water, it provides compelling evidence for a subsurface ocean.

Cassini will continue to study the complex nature of the plume region in the three planned additional flybys of Enceladus. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. More Cassini information is at http://www.nasa.gov/cassini and http://saturn.jpl.nasa.gov . ESA website: http://www.esa.int/esaMI/Cassini-Huygens/

Enceladus' image gallery: http://www.nasa.gov/mission_pages/cassini/multimedia/gallery-indexEnceladus.html

Images, Text, Credits: NASA / ESA / JPL-Caltech / Jia-Rui C. Cook / Space Science Institute.

Greetings, Orbiter.ch

vendredi 1 juin 2012

The successful launch of spacecraft Intelsat-19











Sea Launch logo.

06/01/2012

June 1, 2012 at 9:23:55 GMT from the platform "Sea Launch" was successfully launched rocket "Zenit-2S» to telecommunications spacecraft (SC) "Intelsat-19."

Zenit-3SL rocket launch

Office of the spacecraft from the booster occurred on schedule at 10:23 Moscow time. Satellite Intelsat-19 displayed on the target orbit.

video
 Intelsat 19 launched successfully

The Zenit-3SL rocket carrying the spacecraft lifted off at 22:23 Pacific Daylight Time (PDT) on Thursday, May 31st (05:23 UTC/GMT, Friday, June 1) from the launch platform, positioned at 154 degrees West longitude in the international waters of the Pacific Ocean. One hour later, the Block DM-SL upper stage inserted the satellite, weighing 5,600 kilograms (12,345 lbs.) and built by Space Systems/Loral, into geosynchronous transfer orbit, on its way to a final orbital position at 166 degrees East longitude.

 Intelsat 19 launch

Operators at the Intelsat Launch Control Center acquired the spacecraft's first signals from orbit shortly after spacecraft separation. All systems performed nominally throughout the launch mission.

Sea Launch maritime launch-pad

About Sea Launch AG

Sea Launch AG, headquartered in Bern, Switzerland, provides strategic end–to–end launch solutions to the industry's satellite operator community based on the Zenit launch system. These services include the provision of all–inclusive launch services as well as schedule assurance, financing, risk management; insurance and creative contracting solutions to meet the changing demands of the commercial launch market. Sea Launch AG owns and manages the primary technology, patent and other intellectual property and tangible assets of the company. These include the launch platform Odyssey and the Sea Launch Commander vessels located in the Home Port facility in Long Beach, California, and the unique know–how associated with launching satellites from an ocean–based launch platform located directly on the equator.  Sea Launch AG contracts directly and exclusively with Energia Logistics Ltd. as its technical partner for the delivery and execution of Sea Launch Zenit–3SL launch services.  The Sea Launch system offers the most direct and cost-effective route to geostationary orbit for commercial communications satellites, providing diversity of supply, affordability and flexibility for the industry's satellite operators. For more information, please visit the Sea Launch website at: http://www.sea-launch.com.

About Intelsat

Intelsat-19

Intelsat is the leading provider of satellite services worldwide. For over 45 years, Intelsat has been delivering information and entertainment for many of the world's leading media and network companies, multinational corporations, Internet Service Providers and governmental agencies. Intelsat's satellite, teleport and fiber infrastructure is unmatched in the industry, setting the standard for transmissions of video, data and voice services. From the globalization of content and the proliferation of HD, to the expansion of cellular networks and broadband access, with Intelsat, advanced communications anywhere in the world are closer, by far.

Intelsat-19 Spacecraft Launch Ustream link (video): http://www.ustream.tv/recorded/22995213

Sea Launch video (presentation): http://www.myspace.com/orbiter.ch/videos/video/39584920

Announcement of the Russian Federal Space Agency: http://www.federalspace.ru/main.php?id=2&nid=19154

Images, Video, Text, Credits: Press Service of the Russian Space Agency (Roscosmos PAO) / Sea Launch AG / Translation: Orbiter.ch.

Best regards, Orbiter.ch

Artemis keeps talking the talk






ESA logo.

1 June 2012

Although ESA’s Artemis telecommunications satellite has officially completed its mission, it still has plenty to offer. Reaching its working orbit almost 11 years ago after an arduous journey, Artemis continues to communicate with Earth.

After almost 11 years in orbit, it is a fact that the Artemis mission has been successfully completed. To meet the demand of its operational users, ESA decided to keep operating Artemis for a few more years until its planned deorbiting in 2014.

Artemis artist view

Equipped with a suite of advanced communication payloads, Artemis has scored a long series of satcom firsts still in use today and precursors to new ESA programmes like the European Data Relay System. 

“Artemis has demonstrated technologies that have become standard for many satcom missions and, at the same time, has provided communication services that have exceeded the initial design goals,” said Magali Vaissiere, Director of ESA’s Telecommunications and Integrated Applications.

For example, Artemis created the first laser data link between satellites in different orbits. It was the first telecom satellite to be extensively reprogrammed in orbit, and it was the first to power its way to geostationary orbit, 36 000 km up, with ion thrusters after surviving the longest-ever drift to its destination.

ATV Johannes Kepler

Artemis also provided data relay for Envisat, the largest Earth observation satellite ever built.

Today, Artemis provides links for all of ESA’s Automated Transfer Vehicle (ATV) missions to the International Space Station, from launcher separation to docking, deorbiting and, finally, reentry.

Its navigation payload is a critical element for the European Geostationary Overlay System (EGNOS), which enhances navigation services data for aircraft and ships.

Artemis has been broadcasting the EGNOS signals since 2003 and supports the EGNOS open service and the safety-of-life service.

Artemis

Artemis’ list of accomplishments includes establishing two-way links in 2006 and 2007 with an aircraft flying over the southern coast of France, receiving video footage at 50 Mbits per second.

Artemis also provided a two-way link with an unmanned drone dropped from an altitude of 21 km off the coast of Sardinia in 2007. Telemetry and commands were exchanged while the drone was flying in excess of Mach 1.

“Since joining the Artemis adventure, I have discovered a team of people working with passion for the success of this mission,” said Daniele Galardini, Head of Redu Centre and the Artemis project manager. “Thanks to all, it is an honour to work with them.”

Related links:

Artemis achievements: http://telecom.esa.int/telecom/www/object/index.cfm?fobjectid=424

Artemis: http://telecom.esa.int/telecom/www/area/index.cfm?fareaid=26

Telecommunications and Integrated Applications: http://telecom.esa.int/telecom/www/language/index.cfm?flanguageid=5

More about Redu: http://telecom.esa.int/telecom/www/area/index.cfm?fareaid=62&nocache

Images, Text, Credits: ESA / J. Huart / NASA.

Greetings, Orbiter.ch

jeudi 31 mai 2012

Dragon Returns to Earth












NASA / SpaceX - Cots Demo-2 Mission patch.

May 31, 2012


Image above: Artist's rendition of SpaceX's Dragon spacecraft as it returns to Earth. Dragon's PICA-X heat shield protects the vehicle as it returns to Earth like a burning comet. Credit: SpaceX.

video
SpaceX's Dragon capsule splash down

SpaceX's Dragon capsule splashed down in the Pacific Ocean at 11:42 a.m. EDT a few hundred miles west of Baja California, Mexico, marking a successful end to the first mission by a commercial company to resupply the International Space Station.


Image above: The SpaceX Dragon cargo vehicle floats in the Pacific Ocean after splashdown. Credit: SpaceX.

This mission is a demonstration flight by Space Exploration Technologies, or SpaceX, as part of its contract with NASA to have private companies launch cargo safely to the International Space Station.

For more information about SpaceX Dragon spacecraft Cost Demo-2 Mission, visit: http://www.nasa.gov/exploration/commercial/cargo/spacex_index.html

Images (mentioned), Video, Text, Credits: NASA / NASA TV / SapceX.

Cheers, Orbiter.ch

XMM-Newton reveals light 'echo' around supermassive black hole












ESA - XMM Newton Mission patch.

31 May 2012

Astronomers studying the galaxy NGC 4151 with ESA's XMM-Newton space observatory have detected X-rays emitted and then reflected by ionised iron atoms very close to the supermassive black hole hosted at the galaxy's core. By measuring the time delays occurring in these 'reverberation' events, they were able to map the vicinity of this black hole in unprecedented detail.

Supermassive black holes are enormous concentrations of matter, weighing millions to billions of times the mass of the Sun, that reside at the centre of most large galaxies, including the Milky Way. As they do not emit light, these extremely dense objects can only be detected indirectly, via the effect exerted by their intense gravitational pull on the neighbouring matter. A small fraction of these supermassive black holes feed on material from their surroundings at extraordinary rates, giving rise to intense emission that may even outshine the entire radiation output of their host galaxies. Known as Active Galactic Nuclei (AGN), these sources are a powerful tool used by astronomers to probe the dynamics of matter around the most massive of black holes.


Image above: Galaxy NGC 4151. Credit: David W. Hogg, Michael R. Blanton, and the Sloan Digital Sky Survey Collaboration.

The accretion of matter onto a black hole occurs through a disc of material that spirals around the black hole. Heated by internal friction up to millions of degrees, the accreting matter radiates profusely at ultraviolet and soft X-ray wavelengths. Astronomers invoke the presence of a corona located beyond the disc and populated by highly energetic electrons to explain the observed emission from AGN at hard X-ray wavelengths. Very little is known, though, about the shape and size of the corona, and about the origin of the electrons in the corona.

To investigate the extreme phenomena taking place in the near vicinity of black holes, astronomers studying AGN have been dedicating great efforts to detecting radiation from the innermost parts of the accretion disc and from the corona. An excellent diagnostic of both regions is to search for 'reverberation' – namely the light emitted by the corona and then reflected by the disc. Identifying reverberation events is possible because an AGN's emission is strongly variable, exhibiting flares and other fluctuations on very short time scales. If a burst of light in the corona were to induce excitation in the disc material, thus causing further emission from this region, then the two signals would be detected separated by a time delay. This delay contains valuable information about the path travelled by light from the corona to the disc, and astronomers have long tried to measure it to constrain the size and relative location of these two components.

video

Video above: X-ray light 'echoes' around a black hole. (For further details click here.) Credit: NASA/Goddard Space Flight Center.

"We have now detected the first unequivocal evidence of time delay between emission from the corona and different parts of the disc in an AGN," says Abderahmen Zoghbi from the University of Maryland, USA. Zoghbi led a study of NGC 4151, a galaxy hosting one of the brightest AGN known at X-ray wavelengths, using data from ESA's XMM-Newton X-ray observatory. "The detection of a delay confirms that the corona is clearly separated from the disc, and the amount of delay – a couple of thousand seconds, about half an hour – indicates that it must be compact in size, and located very close to the black hole, above and below the central part of the disc," he adds.

The lag detected in this study was observed in a particular emission line that stands out in AGN spectra, the so-called iron K line. Produced by ionised iron atoms at an energy of about 6.4 keV, this line is one of the best understood features in the X-ray spectra of AGN. "Since we know the physics of the iron K line so well, our detection of delay in its signal is a direct proof of reverberation taking place very close to a supermassive black hole," comments Zoghbi. Previous detections of time delays in other AGN had relied on other, less well understood parts of the spectrum.

video

Video above: Reverberation of X-rays in the vicinity of a black hole. (For further details and an animated sequence click here.) Images and animation courtesy of Abderahmen Zoghbi, University of Maryland, USA.

"Perhaps most interestingly, not only did we detect a delay in the iron K line emission between corona and disc, we were also able to reveal the disc's progressive response," notes co-author Andrew Fabian from the Institute of Astronomy in Cambridge, UK. In fact, a detailed analysis of the line's distorted shape indicated that different delays affect the signal detected at different wavelengths. The most redshifted part of the line, which bears the strongest effects of the black hole's gravity and thus traces emission from the innermost part of the disc, displayed delays of a thousand seconds or less. Delays in the blueshifted part of the line, caused by emission from the outer disc, were significantly longer, up to 2000 seconds. "This allowed us to follow the 'echo' of the burst of light from the corona as it gradually illuminated the entire disc, making it shine at the wavelengths of the iron K line," Fabian adds.

 XMM-Newton spacecraft

Zoghbi and his collaborators are now repeating the same analysis on other AGN-hosting galaxies. Detecting reverberation-induced delays in a larger sample of sources will provide astronomers with a comprehensive dataset to study matter accretion onto black holes in unprecedented detail and, ultimately, to test general relativity in one of its strongest regimes.

"This study has finally uncovered a long-sought-after aspect of AGN that unambiguously reveals their innermost regions," comments Norbert Schartel, XMM-Newton Project Scientist at ESA. "Observations are now beginning to disclose what happens in the 'backyard' of a black hole, allowing us to sharpen our understanding of these fascinating objects."

Notes for editors

The findings presented here are based on several observations of the galaxy NGC 4151 performed with ESA's XMM-Newton space observatory at energies between 2 and 10 keV.

NGC 4151 is a well-studied Seyfert galaxy, hosting one of the brightest active galactic nuclei (AGN) known at X-ray wavelengths. The supermassive black hole lying at the centre of NGC 4151 has a mass of about 50 million solar masses.

The emission spectrum of an AGN in the X-ray band (divided into soft X-rays, between 100 eV and 10 keV, and hard X-rays, between 10 and 100 keV) is characterised by three main components: emission from the accretion disc, which dominates up to a few 100 eV; emission from Compton up-scattering of photons from the disc in the corona, which dominates up to a few tens of keV; reflection of high-energy photons from the corona off the disc material, resulting in hard X-ray emission that dominates the spectrum up to 100 keV or more.

Reflection off the disc also gives rise to fluorescence, or line emission from a number of heavy elements present in the disc. Among the several fluorescent lines in AGN spectra, the most prominent is the so-called iron K line, corresponding to an energy of 6.4 keV; this is a combined effect of the relatively large abundance of iron in the Universe and of the high efficiency of this particular emission process.

The iron K line has an intrinsically narrow profile. However, when the line arises from iron ions in the accretion disc around a black hole, its shape is affected by relativistic effects induced by the black hole's strong gravitational field. Thus, in an AGN spectrum, the iron K line appears distorted, broadened and shifted to slightly lower energies. With the aid of the general theory of relativity, it is possible to quantify the distortion that will affect the line emitted by an iron ion at a certain distance from a black hole of a given mass. Astronomers can use distortions observed in the iron K line's shape to probe the entire extent of a black hole's accretion disc. This crucial aspect was exploited in the study of NGC 4151.

Related publication:

A. Zoghbi, et al., 'Relativistic iron K X-ray reverberation in NGC 4151', Monthly Notices of the Royal Astronomical Society, 422, 129–134. DOI: 10.1111/j.1365-2966.2012.20587.x

For more information about XMM Newton, visit: http://xmm.esac.esa.int/

Images, Videos, Text, Credits: ESA / David W. Hogg, Michael R. Blanton, and the Sloan Digital Sky Survey Collaboration / Abderahmen Zoghbi, University of Maryland, USA / NASA/Goddard Space Flight Center.

Greetings, Orbiter.ch

ALMA Turns its Eyes to Centaurus A












ESO - European Southern Observatory logo.

31 May 2012

 The radio galaxy Centaurus A, as seen by ALMA

A new image of the centre of the distinctive galaxy Centaurus A, made with the Atacama Large Millimeter/submillimeter Array (ALMA), shows how the new observatory allows astronomers to see through the opaque dust lanes that obscure the galaxy’s centre, with unprecedented quality. ALMA is currently in its Early Science phase of observations and is still under construction, but is already the most powerful telescope of its kind. The observatory has just issued the Call for Proposals for its next cycle of observations, in which the growing telescope will have increased capabilities.

The radio galaxy Centaurus A, as seen by ALMA (mouseover comparison): http://www.eso.org/public/images/comparisons/eso1222a/

Centaurus A [1] is a massive elliptical radio galaxy — a galaxy which emits strong radio waves — and is the most prominent, as well as by far the nearest, radio galaxy in the sky [2]. Centaurus A has therefore been observed with many different telescopes. Its very luminous centre hosts a supermassive black hole with a mass of about 100 million times that of the Sun.

In visible light, a characteristic feature of the galaxy is the dark band that obscures its centre (see for example eso1221). This dust lane harbours large amounts of gas, dust and young stars. These features, together with the strong radio emission, are evidence that Centaurus A is the result of a collision between a giant elliptical galaxy, and a smaller spiral galaxy whose remains form the dusty band.

The strange galaxy Centaurus A in the constellation of Centaurus

To see through the obscuring dust in the central band, astronomers need to observe using longer wavelengths of light. This new image of Centaurus A combines observations at wavelengths around one millimetre, made with ALMA, and observations in near-infrared light. It thus provides a clear view through the dust towards the galaxy’s luminous centre.

The new ALMA observations, shown in a range of green, yellow and orange colours, reveal the position and motion of the clouds of gas in the galaxy. They are the sharpest and most sensitive such observations ever made. ALMA was tuned to detect signals with a wavelength around 1.3 millimetres, emitted by molecules of carbon monoxide gas. The motion of the gas in the galaxy causes slight changes to this wavelength, due to the Doppler effect [3]. The motion is shown in this image as changes in colour. Greener features trace gas coming towards us while more orange features depict gas moving away. We can see that the gas to the left of the centre is moving towards us, while the gas to the right of the centre is moving away from us, indicating that the gas is orbiting around the galaxy.

video
Zooming in on the radio galaxy Centaurus A, as seen by ALMA

The ALMA observations are overlaid on a near-infrared image of Centaurus A obtained with the SOFI instrument attached to the ESO New Technology Telescope (NTT). The image was processed using an innovative technique that removes the screening effect of the dust (eso0944). We see a clear ring of stars and clusters glowing in a golden colour, the tattered remains of the spiral galaxy being ripped apart by the gravitational pull of the giant elliptical galaxy.

The alignment between the ring of stars seen by the NTT in infrared light and the gas seen by ALMA at millimetre wavelengths highlights different aspects of similar structures in the galaxy. This is an example of how observations with other telescopes can complement these new observations from ALMA.

video
Panning over the radio galaxy Centaurus A, as seen by ALMA

Construction of ALMA, on the Chajnantor Plateau in northern Chile, will be completed in 2013, when 66 high-precision antennas will be fully operational. Half of the antennas have already been installed (see ann12035). Early scientific observations with a partial array began in 2011 (see eso1137), and are already producing outstanding results (see for example eso1216). The ALMA observations of Centaurus A shown here were taken as part of the Commissioning and Science Verification phase of the telescope.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA is funded in Europe by the European Southern Observatory (ESO), in North America by the U.S. National Science Foundation (NSF) in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and in East Asia by the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Academia Sinica (AS) in Taiwan. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), which is managed by Associated Universities, Inc. (AUI) and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

Notes:

[1] This galaxy is called Centaurus A because it was the first major source of radio waves discovered in the constellation of Centaurus, in the 1950s. It is also referred as NGC 5128. The galaxy was discovered by British astronomer James Dunlop on 4 August 1826.

[2] Centaurus A lies about 12 million light-years away in the southern constellation of Centaurus (The Centaur).

[3] The Doppler effect is the change in wavelength of a wave for an observer moving relative to the source of the wave. Molecules in gas clouds in space emit light at well-defined wavelengths, and so the motion of these clouds leads to slight changes in the wavelengths that are detected.

More information:

The year 2012 marks the 50th anniversary of the founding of the European Southern Observatory (ESO). ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Links:

    ESO ALMA pages: http://www.eso.org/public/teles-instr/alma.html

    Joint ALMA Observatory: http://www.almaobservatory.org/

    Pictures of ALMA: http://www.eso.org/public/images/archive/category/alma/

Images, Text, Credits: ALMA (ESO/NAOJ/NRAO); ESO/Y. Beletsky/IAU and Sky & Telescope/Videos: ALMA (ESO/NAOJ/NRAO); ESO; Y. Beletsky; Nick Risinger (skysurvey.org). Music: Disasterpeace (http://disasterpeace.com/).

Cheers, Orbiter.ch

NASA - ESA Hubble Shows Milky Way is Destined for Head-On Collision











NASA - Hubble Space Telescope patch.

May 31, 2012

NASA astronomers announced Thursday they can now predict with certainty the next major cosmic event to affect our galaxy, sun, and solar system: the titanic collision of our Milky Way galaxy with the neighboring Andromeda galaxy.

The Milky Way is destined to get a major makeover during the encounter, which is predicted to happen four billion years from now. It is likely the sun will be flung into a new region of our galaxy, but our Earth and solar system are in no danger of being destroyed.


Image above: This illustration shows a stage in the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy, as it will unfold over the next several billion years. In this image, representing Earth's night sky in 3.75 billion years, Andromeda (left) fills the field of view and begins to distort the Milky Way with tidal pull. (Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas; and A. Mellinger).

"Our findings are statistically consistent with a head-on collision between the Andromeda galaxy and our Milky Way galaxy," said Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore.

The solution came through painstaking NASA Hubble Space Telescope measurements of the motion of Andromeda, which also is known as M31. The galaxy is now 2.5 million light-years away, but it is inexorably falling toward the Milky Way under the mutual pull of gravity between the two galaxies and the invisible dark matter that surrounds them both.

video

This animation depicts the collision between our Milky Way galaxy and the Andromeda galaxy. Hubble Space Telescope observations indicate that the two galaxies, pulled together by their mutual gravity, will crash together about 4 billion years from now. Around 6 billion years from now, the two galaxies will merge to form a single galaxy. The video also shows the Triangulum galaxy, which will join in the collision and perhaps later merge with the Andromeda/Milky Way pair. (Visualization Credit: NASA; ESA; and F. Summers, STScI | Simulation Credit: NASA; ESA; G. Besla, Columbia University; and R. van der Marel, STScI).

"After nearly a century of speculation about the future destiny of Andromeda and our Milky Way, we at last have a clear picture of how events will unfold over the coming billions of years," said Sangmo Tony Sohn of STScI.

The scenario is like a baseball batter watching an oncoming fastball. Although Andromeda is approaching us more than 2,000 times faster, it will take 4 billion years before the strike.

Computer simulations derived from Hubble's data show that it will take an additional two billion years after the encounter for the interacting galaxies to completely merge under the tug of gravity and reshape into a single elliptical galaxy similar to the kind commonly seen in the local universe.

Although the galaxies will plow into each other, stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today.

To make matters more complicated, M31's small companion, the Triangulum galaxy, M33, will join in the collision and perhaps later merge with the M31/Milky Way pair. There is a small chance that M33 will hit the Milky Way first.


Image above: This illustration shows the collision paths of our Milky Way galaxy and the Andromeda galaxy. The galaxies are moving toward each other under the inexorable pull of gravity between them. Also shown is a smaller galaxy, Triangulum, which may be part of the smashup. (Credit: NASA; ESA; A. Feild and R. van der Marel, STScI).

The universe is expanding and accelerating, and collisions between galaxies in close proximity to each other still happen because they are bound by the gravity of the dark matter surrounding them. The Hubble Space Telescope's deep views of the universe show such encounters between galaxies were more common in the past when the universe was smaller.

A century ago astronomers did not realize that M31 was a separate galaxy far beyond the stars of the Milky Way. Edwin Hubble measured its vast distance by uncovering a variable star that served as a "milepost marker."

Hubble went on to discover the expanding universe where galaxies are rushing away from us, but it has long been known that M31 is moving toward the Milky Way at about 250,000 miles per hour. That is fast enough to travel from here to the moon in one hour. The measurement was made using the Doppler effect, which is a change in frequency and wavelength of waves produced by a moving source relative to an observer, to measure how starlight in the galaxy has been compressed by Andromeda's motion toward us.

Previously, it was unknown whether the far-future encounter will be a miss, glancing blow, or head-on smashup. This depends on M31’s tangential motion. Until now, astronomers had not been able to measure M31's sideways motion in the sky, despite attempts dating back more than a century. The Hubble Space Telescope team, led by van der Marel, conducted extraordinarily precise observations of the sideways motion of M31 that remove any doubt that it is destined to collide and merge with the Milky Way.

"This was accomplished by repeatedly observing select regions of the galaxy over a five- to seven-year period," said Jay Anderson of STScI.

"In the worst-case-scenario simulation, M31 slams into the Milky Way head-on and the stars are all scattered into different orbits," said Gurtina Besla of Columbia University in New York, N.Y. "The stellar populations of both galaxies are jostled, and the Milky Way loses its flattened pancake shape with most of the stars on nearly circular orbits. The galaxies' cores merge, and the stars settle into randomized orbits to create an elliptical-shaped galaxy."


This series of photo illustrations shows the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy.

    - First Row, Left: Present day.
    - First Row, Right: In 2 billion years the disk of the approaching Andromeda galaxy is noticeably larger.
    - Second Row, Left: In 3.75 billion years Andromeda fills the field of view.
    - Second Row, Right: In 3.85 billion years the sky is ablaze with new star formation.
    - Third Row, Left: In 3.9 billion years, star formation continues.
    - Third Row, Right: In 4 billion years Andromeda is tidally stretched and the Milky Way becomes warped.
    - Fourth Row, Left: In 5.1 billion years the cores of the Milky Way and Andromeda appear as a pair of bright lobes.
    - Fourth Row, Right: In 7 billion years the merged galaxies form a huge elliptical galaxy, its bright core dominating the nighttime sky.

(Credit: NASA; ESA; Z. Levay and R. van der Marel, STScI; T. Hallas, and A. Mellinger)

The space shuttle servicing missions to Hubble upgraded it with ever more-powerful cameras, which have given astronomers a long-enough time baseline to make the critical measurements needed to nail down M31's motion. The Hubble observations and the consequences of the merger are reported in three papers that will appear in an upcoming issue of the Astrophysical Journal.

For more images, video and information about M31's collision with the Milky Way, visit: http://hubblesite.org/news/2012/20

Images (mentioned), Video (mentioned), Text, Credit: NASA.

Greetings, Orbiter.ch

LHC data harvest continues in earnest












CERN - European Organization for Nuclear Research logo.

31 May 2012


Image above: Experimental physicists from the ATLAS experiment discussing their work at CERN. More data means more analysis work for physicists.


The Large Hadron Collider is busy supplying the experiments with an impressive number of collisions at an energy of 4 TeV per beam. After just 2 months of beam this year the LHC has already delivered 7 inverse femtobarns of data – more than the entire 2011 run.
An inverse femtobarn is a measure of integrated luminosity – or the amount of data that experiments can gather. An inverse femtobarn represents about 100 million million collisions.
The LHC has also beaten peak luminosity records, reaching 6,6 × 1033 cm -2 s -1 on 26 May, compared to last year's maximum of 3,6 × 1033 cm -2 s -1.
The accumulation of large amounts of data from collisions is crucial to increasing the chances of discoveries at the LHC.

 Note:

CERN, the European Organization for Nuclear Research, is one of the world’s largest and most respected centres for scientific research. Its business is fundamental physics, finding out what the Universe is made of and how it works. At CERN, the world’s largest and most complex scientific instruments are used to study the basic constituents of matter — the fundamental particles. By studying what happens when these particles collide, physicists learn about the laws of Nature.

The instruments used at CERN are particle accelerators and detectors. Accelerators boost beams of particles to high energies before they are made to collide with each other or with stationary targets. Detectors observe and record the results of these collisions.

Founded in 1954, the CERN Laboratory sits astride the Franco–Swiss border near Geneva. It was one of Europe’s first joint ventures and now has 20 Member States.

More information:

Quantum Diaries archive: Why don't we just say collision rate?:
http://www.quantumdiaries.org/2011/03/02/why-don%E2%80%99t-we-just-say-collision-rate/

Image, Text, Credit: CERN.

Best regards, Orbiter.ch

Electric Moon Jolts the Solar Wind














NASA - STEREO Mission logo / NASA / ESA - ARTEMIS Mission logo.

May 31, 2012

With the moon as the most prominent object in the night sky and a major source of an invisible pull that creates ocean tides, many ancient cultures thought it could also affect our health or state of mind – the word "lunacy" has its origin in this belief. Now, a powerful combination of spacecraft and computer simulations is revealing that the moon does indeed have a far-reaching, invisible influence – not on us, but on the Sun, or more specifically, the solar wind.

The solar wind is a thin stream of electrically conducting gas called plasma that's constantly blown off the surface of the Sun in all directions at around a million miles per hour. When a particularly fast, dense or turbulent solar wind strikes Earth's magnetic field, it can generate magnetic and radiation storms that are capable of disrupting satellites, power grids, and communication systems. The magnetic "bubble" surrounding Earth also pushes back on the solar wind, creating a bow shock tens of thousands of miles across over the day side of Earth where the solar wind slams into the magnetic field and abruptly slows from supersonic to subsonic speed.


Image above: This is a view of the moon transiting, or passing in front of, the Sun as seen from the STEREO-B spacecraft on Feb. 25, 2007. The Sun is in false color, and the moon appears as a black disk on the upper right. NASA's STEREO mission consists of two spacecraft launched in October, 2006 to study solar storms. Credit: NASA.

Unlike Earth, the moon is not surrounded by a global magnetic field. "It was thought that the solar wind crashes into the lunar surface without any warning or 'push back' on the solar wind," says Dr. Andrew Poppe of the University of California, Berkeley. Recently, however, an international fleet of lunar-orbiting spacecraft has detected signs of the moon's presence "upstream" in the solar wind. "We've seen electron beams and ion fountains over the moon's day side," says Dr. Jasper Halekas, also of the University of California, Berkeley.

These phenomena have been seen as far as 10,000 kilometers (6,214 miles) above the moon and generate a kind of turbulence in the solar wind ahead of the moon, causing subtle changes in the solar wind's direction and density. The electron beams were first seen by NASA's Lunar Prospector mission, while the Japanese Kaguya mission, the Chinese Chang'e mission, and the Indian Chandrayaan mission all saw ion plumes at low altitudes. NASA's ARTEMIS mission has now also seen both the electron beams and the ion plumes, plus newly identified electromagnetic and electrostatic waves in the plasma ahead of the moon, at much greater distances from the moon. "With ARTEMIS, we can see the plasma ring and wiggle a bit, surprisingly far away from the moon," says Halekas. ARTEMIS stands for "Acceleration, Reconnection, Turbulence and Electrodynamics of the Moon’s Interaction with the Sun".


Image above: This is an artist's concept of the Earth's global magnetic field, with the bow shock. Earth is in the middle of the image, surrounded by its magnetic field, represented by purple lines. The bow shock is the blue crescent on the right. Many energetic particles in the solar wind, represented in gold, are deflected by Earth's magnetic "shield". Credit: Walt Feimer (HTSI)/NASA/Goddard Space Flight Center Conceptual Image Lab.

"An upstream turbulent region called the 'foreshock' has long been known to exist ahead of the Earth's bow shock, but the discovery of a similar turbulent layer at the moon is a surprise," said Dr. William Farrell of NASA's Goddard Space Flight Center in Greenbelt, Md. Farrell is lead of the NASA Lunar Science Institute's Dynamic Response of the Environment At the Moon (DREAM) lunar science center, which contributed to the research.

Computer simulations help explain these observations by showing that a complex electric field near the lunar surface is generated by sunlight and the flow of the solar wind. The simulation reveals this electric field can generate electron beams by accelerating electrons blasted from surface material by solar ultraviolet light. Also, related simulations show that when ions in the solar wind collide with ancient, "fossil" magnetic fields in certain areas on the lunar surface, they are reflected back into space in a diffuse, fountain-shaped pattern. These ions are mostly the positively charged ions (protons) of hydrogen atoms, the most common element in the solar wind.

"It's remarkable that electric and magnetic fields within just a few meters (yards) of the lunar surface can cause the turbulence we see thousands of kilometers away," says Poppe. When exposed to solar winds, other moons and asteroids in the solar system should have this turbulent layer over their day sides as well, according to the team.

"Discovering more about this layer will enhance our understanding of the moon and potentially other bodies because it allows information about conditions very near the surface to propagate to great distances, so a spacecraft will gain the ability to virtually explore close to these objects when it's actually far away," said Halekas.

The research is described in a series of six papers recently published by Poppe, Halekas, and their colleagues at NASA Goddard, U.C. Berkeley, U.C. Los Angeles, and the University of Colorado at Boulder in Geophysical Research Letters and the Journal of Geophysical Research. The research was funded by NASA's Lunar Science Institute, which is managed at NASA's Ames Research Center, Moffett Field, Calif., and oversees the DREAM lunar science center.

Related links:

NASA's Lunar Science Institute: http://lunarscience.nasa.gov/

Dynamic Response of the Environment At the Moon (DREAM) lunar science center: http://ssed.gsfc.nasa.gov/dream/

ARTEMIS mission: http://www.nasa.gov/mission_pages/artemis/

Images (mentioned), Text, Credit: NASA / Bill Steigerwald.

Greetings, Orbiter.ch

Dream Chaser Flight Vehicle Scales Rocky Mountain Summits












Commercial Crew Program patch.

May 31, 2012

Sierra Nevada Corporation (SNC) Space Systems' Dream Chaser design passed one of its most complex tests to date with a successful captive-carry test conducted near the Rocky Mountain Metropolitan Airport in Jefferson County, Colo., on May 29.

video
CCP: Sierra Nevada Captive-Carry Test

Just like the space shuttle before it, SNC's Dream Chaser will go through extensive testing to prove its wings will work. The company built a full-scale flight vehicle of the Dream Chaser spacecraft to carry out the evaluations.

Backdropped by skyscraping summits, an Erickson Air-Crane helicopter lifted the full-scale orbital crew vehicle to verify proper aerodynamic flight performance. Future plans call for the flight vehicle to be released to evaluate the design's handling during the landing phase of a mission.

The captive-carry test marks the completion of another milestone for the Dream Chaser Space System as part of the Commercial Crew Development Round 2 (CCDev2) agreement with NASA's Commercial Crew Program (CCP).


Image above: Sierra Nevada Corporation (SNC) Space Systems' Dream Chaser flight vehicle is lifted by an Erickson Air-Crane helicopter near the Rocky Mountain Metropolitan Airport in Jefferson County, Colo., on May 29, during a captive-carry test.
Image credit: Sierra Nevada Corporation (SNC).

"This is a very positive success for the Dream Chaser team and their innovative approach. I applaud and encourage the designers and engineers to continue their efforts in meeting the objectives of the rest of their CCDev2 milestones," said Ed Mango, CCP program manager.

SNC is one of seven companies working to develop commercial crew transportation capabilities to ferry U.S. astronauts to and from low Earth orbit and the International Space Station. The Dream Chaser is designed to carry as many as seven astronauts to space, and is the only spacecraft under CCDev2 that incorporates wings and is designed to land on a conventional runway.

"The successful captive-carry flight test of the Dream Chaser full-scale flight vehicle marks the beginning of SNC's flight test program; a program that could culminate in crewed missions to the International Space Station for NASA," said Steve Lindsey, former NASA astronaut and head of Dream Chaser's flight operations for SNC.

Before the company took to the Rocky Mountain skies, it conducted an interface test to demonstrate the release mechanism between the Dream Chaser prototype and the heavy-lift helicopter. It also conducted a ground-based landing gear drop test and a thorough flight test readiness review with engineers, technical experts and representatives from SNC and NASA.

video
Commercial Crew Program

Another recent milestone included an evaluation of the separation system compatibility of Dream Chaser with its initial launch vehicle, the United Launch Alliance Atlas V rocket, which would be used to release the spacecraft from the rocket’s second stage after it has placed the spacecraft into low Earth orbit.

Data from the captive-carry test will provide the company an early opportunity to evaluate and prove hardware, facilities and ground operations in preparation for approach and landing tests scheduled for later this year.

All of NASA’s CCDev2 partners, including SNC, continue to meet their established milestones in developing commercial crew transportation capabilities.

For more information about NASA's Commercial Crew Program, visit: http://www.nasa.gov/commercialcrew

Image, Videos, Text, Credits: NASA / Rebecca Regan / Sierra Nevada Corporation (SNC).

Cheers, Orbiter.ch

Dragon Capsule Released from Station












NASA / SpaceX - Cots Demo-2 Mission patch.

31 May 2012

video
 Dragon Departs the Station

The SpaceX Dragon capsule was released from the International Space Station’s robotic arm by crew members of Expedition 31 at 5:49 a.m. EDT. The capsule now will begin a series of departure burns and maneuvers to move beyond the 656-foot (200-meter) “keep out sphere” around the station and begin its return trip to Earth. NASA TV coverage will resume at 10:15 a.m. to follow the capsule’s deorbit and splashdown. The capsule is currently scheduled to splashdown in the Pacific Ocean at 11:44 a.m., hundreds of miles west of Baja California. A news briefing will be held jointly from Johnson and SpaceX in Hawthorne, Calif., at 2 p.m. live on NASA TV.


Image above: The SpaceX Dragon cargo vehicle is released by the station's robotic arm for return to Earth. Image credit: NASA TV.

This mission is a demonstration flight by Space Exploration Technologies, or SpaceX, as part of its contract with NASA to have private companies launch cargo safely to the International Space Station.

For more information about SpaceX Dragon spacecraft Cost Demo-2 Mission, visit: http://www.nasa.gov/exploration/commercial/cargo/spacex_index.html

Image, Video, Text, Credits: NASA / NASA TV / SpaceX.

Greetings, Orbiter.ch

mercredi 30 mai 2012

Rosetta flyby uncovers the complex history of asteroid Lutetia












ESA - Rosetta Mission patch.

30 May 2012

The long and tumultuous history of asteroid (21) Lutetia is revealed by a comprehensive analysis of the data gathered by ESA's Rosetta spacecraft when it flew past this large main-belt asteroid on 10 July 2010. New studies have revealed the asteroid's surface morphology, composition and other properties in unprecedented detail. In particular, extensive studies of Lutetia's geological features have opened a unique window into the complex history of this peculiar object.

video

Video above: Asteroid (21) Lutetia as seen by Rosetta in July 2010. Credit: ESA 2012 MPS for OSIRIS Team MPS/ UPD/ LAM/ IAA/ RSSD/ INTA/ UPM/ DASP/ IDA.

On its way to rendezvous with comet 67P/Churyumov-Gerasimenko, ESA's Rosetta spacecraft flew by the main-belt asteroid (21) Lutetia, reaching the closest approach, at a distance of about 3170 km, on 10 July 2010. From this unique vantage point, Rosetta gathered high-resolution images, spectra, and other data, providing scientists with a valuable dataset with which to probe this peculiar asteroid in great detail.

The first results from the flyby, published in late 2011, revealed the mass and volume of Lutetia, leading to an estimate of the asteroid's density, which turned out to be surprisingly high. Data from the flyby also suggested that Lutetia is a primordial planetesimal formed during the very early phases of the Solar System. These and other findings called for further investigations about the nature and history of Lutetia.

"The images collected by Rosetta during the flyby have uncovered, for the first time, the wide variety of craters and other geological features that scar the surface of Lutetia," notes Rita Schulz, Rosetta Project Scientist at ESA. "Scientists have explored this rich pool of data thoroughly in order to characterise many of Lutetia's properties, from its surface morphology and composition to its shape and internal structure, revealing its underlying geological history," she adds. The results of these studies are reported in a series of 21 papers published in a special issue of the journal Planetary and Space Science.

The OSIRIS camera on Rosetta has surveyed the part of Lutetia that was visible during the flyby – about half of its entire surface, mostly coinciding with the asteroid's northern hemisphere. These unique, close-up images have allowed scientists to identify regions characterised by very distinct geological properties with an accuracy of a few hundred metres.

Counting craters is a powerful tool that is used to compare the regions and to uncover their past history. By recording the number, spatial distribution, shapes and sizes of the hundreds of craters that mark the surface of each region, it is possible to date the epoch when these craters were produced by collisions with smaller bodies. In the case of the largest craters, it is even possible to reconstruct the details of the impact that created them.


Image above: Regions on Lutetia's surface. (Click on the image for further details.) Credit: from Thomas et al., Planetary and Space Science Special Issue, 2012.

By tracing craters and other features on Lutetia's surface, scientists have put together a geological map for the asteroid. Their studies have shown that Lutetia's surface comprises regions spanning a wide range of ages: each of them reveals a chapter in the long and tumultuous history of this asteroid.

At one end of this age spectrum, the two heavily cratered Achaia and Noricum regions represent the most ancient portions on the surface of Lutetia: with ages between 3.4 and 3.7 billion years or more, they are almost as old as the asteroid itself. Some of the craters that densely populate these two regions date back to an early epoch in the Solar System's history, right after the so-called Late Heavy Bombardment, when the flux of bodies impacting asteroids, planets and their satellites was significantly larger than it is at present.

Massilia, the largest crater identified on the asteroid, is located in a younger region named Narbonensis. With a diameter of 57 km, this crater provides evidence of the most dramatic event in the history of Lutetia: numerical simulations suggest that the 'projectile' responsible for producing this very wide crater was quite large, with a diameter of about 7.5 km. However, the probability of such a large body colliding with the asteroid is quite low, and so this must have occurred when Lutetia was relatively young.


Image above: Simulation of the formation of a large crater on Lutetia. (Click on the image for further details.) Credit: from Cremonese et al., Planetary and Space Science Special Issue, 2012.

The youngest patch on the surface of Lutetia is the Baetica region, located in the vicinity of the asteroid's North Pole. This region hosts a number of superimposed craters, named the North Polar Crater Cluster (NPCC), which include three large ones with sizes exceeding 10 km. These craters represent the signature left by a series of subsequent impacts that took place quite recently on geological timescales – namely, in the last few hundred million years.

The smooth appearance of the craters in Baetica, which have not been dotted yet with many smaller craters, indicate that its surface is much younger than the heavily battered areas of Lutetia. Furthermore, this region still bears signs of the events that created the NPCC, as indicated by the ejecta that were released during the impacts and then spread on the surrounding area, rather than leaving the asteroid's surface, as a result of its relatively strong gravitational pull. The presence of these 'fresh' deposits, which include many large boulders with sizes up to 300 metres, is another hint at this region's young age.

In addition to craters, other geological markers, such as lineaments and faults, represent an important window into the turbulent past of asteroids and other Solar System bodies. The remarkable images collected by OSIRIS during the flyby have revealed an intricate network of linear features covering long distances across Lutetia's surface, up to 80 km in some cases. Many of these features are the results of seismic phenomena that also caused deformations on pre-existing craters. Lineaments and faults have been mostly detected in the oldest portions of Lutetia's surface. In contrast, a lack of such features in the young region near the North Pole  suggests that the recent impacts that gave rise to the NPCC did not cause significant fractures on the surface of the asteroid.


Image above: The boundary between Baetica and Noricum region on Lutetia. (Click on the image for further details.)  Credit: from Thomas et al., Planetary and Space Science Special Issue, 2012.

Prior to the flyby, one of the most puzzling aspects of Lutetia was its surface composition: different datasets have hinted at either a metallic or a chondritic composition, thus making the classification of this asteroid particularly problematic. Scientists have now addressed the issue by combining data gathered with four remote-sensing instruments on Rosetta – OSIRIS, VIRTIS, MIRO, and ALICE – which cover visible, infrared, microwave and ultraviolet wavelengths. The new data show that Lutetia has an unusual surface composition that does not fit into the schemes established before the flyby and may result from the complex collision history of the asteroid.

The peculiar composition of Lutetia, when considered along with its high density, raises the possibility that this asteroid might have a partially differentiated structure, with a metallic core overlain by a primitive chondritic crust. The only other differentiated asteroid that has been visited by a spacecraft is Vesta, one of the largest asteroids in the Solar System and significantly larger than Lutetia. Whereas it is reasonable to expect such an internal structure in asteroids as large as Vesta, it is still unclear whether this should be the case also for objects of Lutetia's size. Therefore the possible evidence of a differentiated structure suggested by the new data is particularly intriguing.

The flyby of Lutetia also provided a rare opportunity to obtain 'in situ' measurements of the surrounding environment of the asteroid, allowing scientists to search for an exosphere, an internal magnetic field or satellites. All three searches did not find significant evidence for any of these possibilities, and could only set upper limits.

"The data collected during Rosetta's flyby of Lutetia have provided us with a brand new view on this intriguing object," comments Schulz. "I expect that scientists will continue to investigate these unique and extraordinary data for years to come, pushing forward our knowledge about this asteroid and its origin, and revealing new details about the Solar System's past history," she adds.

In the meantime, Rosetta proceeds towards its final destination, comet 67P/Churyumov-Gerasimenko, which will be reached in 2014. "We are eagerly awaiting the next and probably most exciting phase of the mission," concludes Schulz.

Related publication:

Rosetta Fly-by at Asteroid (21) Lutetia. Special issue of Planetary and Space Science, Volume 66, Issue 1, Pages 1-212 (June 2012)

Notes for editors

On its 10-year journey towards comet 67P/Churyumov-Gerasimenko, ESA's Rosetta spacecraft has flown past two main-belt asteroids: (2867) Steins in 2008, and (21) Lutetia in 2010. The flyby of Lutetia took place on 10 July 2010, when Rosetta flew past the asteroid at a distance of 3168.2 km and at a relative speed of 15 km/s.

Most of the scientific instruments on Rosetta were switched on as the spacecraft approached the rotating asteroid, resulting in imaging and spectral observations covering a spectral range from ultraviolet to microwave radiation, and a number of in-situ measurements of the asteroid's environment.

The Optical, Spectroscopic and Infrared Remote Imaging System (OSIRIS) returned 462 pictures of the illuminated northern hemisphere of Lutetia through both its narrow-angle camera (NAC) and wide-angle camera (WAC). These images cover more than 50 per cent of the asteroid's surface and were instrumental in revealing its surface in unprecedented detail.

The ALICE, VIRTIS and MIRO instruments were used to gather spectra at ultraviolet, infrared and microwave wavelengths, respectively, in order to probe the chemical composition of Lutetia's surface.

In-situ searches for an exosphere were conducted with the ROSINA instrument; spectra from the COSAC/Philae, Ptolemy/Philae and ALICE instruments were also used to search for the asteroid's exosphere. Magnetic field measurements were performed with the ROMAP, RPC-MAG/OB and RPC-MAG/IB sensors.

RELATED LINK:

Rosetta at the Planetary Science Archive: http://www.rssd.esa.int/index.php?project=PSA&page=rosetta

Images (mentioned), Video (mentioned), Credit: ESA Rosetta Project Scientist / Rita Schulz.

Greetings, Orbiter.ch